This invention relates to heat curable organopolysiloxane compositions which are cured through hydrosilylation. In more detail, this invention relates to heat curable organopolysiloxane compositions which possess a superior stability during storage and a rapid curability at high temperature.
Organopolysiloxane compositions of an addition type, which utilize hydrosilylation, characteristically produce few reaction by-products and the reaction proceeds rapidly with depth. Therefore, they have been utilized in a wide variety of fields as an adhesive sealing material, a potting material, a coating material for electric and electronic parts, as an adhesive gasket with a factory applied seal for construction use, and as a peelable coating material for papers and films.
However, these organopolysiloxane compositions are extremely unstable during storage. Therefore, one disadvantage is that they can not be stored with all the components in a single container. Due to this instability, the following problems arise: each of the components usually need to be stored in separate containers and two or three components of the composition must be weighed, mixed and defoamed prior to usage.
Conventional approaches proposed to solve these problems were to control the catalytic activity of the hydrosilylation catalysts, especially the platinum type catalysts.
One of the methods proposed is to utilize additives which can control the catalytic activities of the platinum type catalysts. Examples of additives are: acetylene type compounds (U.S. Pat. No. 3,445,420), organosiloxanes containing a CH.sub.2 =CHRSiO unit (where R is a monovalent hydrocarbon group which does not contain. unsaturated fat type hydrocarbons) (Japanese patent application Kokoku, examined, 48-10947), ionic compounds of heavy metals (U.S. Pat. No. 3,532,649), benzotriazole type compounds, and hydroperoxide compounds. However, the stability during storage achieved by the addition of these compounds is off set by a lowering in curing properties and by a lengthening of the time required for curing.
The second method is to isolate the hydrosilylation catalysts from the other reactive components of the composition until the time of heat curing. The proposed method aims to isolate the hydrosilylation catalysts, such as a 2-ethyl hexanol solution of chloroplatinic acid and platinum alkenyl siloxane catalysts, by encapsulating them as a single nucleus or multiple nuclei within thermoplastic resins with a softening point (Japanese patent application Kokoku, examined, 53-41707, Japanese patent application Kokai, laid open, 64-47442, and Japanese patent application Kokoku, examined, 4-46962).
Even with this said method, however, uniformly cured products are not easily prepared when the resin used as a wall material of the capsules has a poor compatibility with silicone. This results in good curing in the area surrounding the catalyst capsules but not in those areas distant from them. Further, when the wall material is a silicone resin which is softened and becomes compatible with silicone upon being heated, the boundary of the catalyst capsules tend to start gelation after storage at room temperature for a long time period, due to a slow releasing property specific to silicone. In addition, the absolute amount of the catalyst capsules necessary for the hydrosilylation is so small in relation to the amount of the composition, that their uniform dispersion is difficult. As a result, the formation of crosslinking does not proceed uniformly after heating, which often disadvantageously results in products containing sections of low hardness and exhibiting a large permanent deformation by compression.
Therefore, an object of this invention is to provide heat curable organopolysiloxane compositions which possess a superior stability during room temperature storage over a long time period, a high curing speed at high temperature, and the capability for uniform crosslinking.
Upon further study of the specification and appended claims, further objects and advantages of this invention will become apparent to those skilled in the art.